1. Field of the Invention:
The present invention relates to a rotary piston engine and, more particularly, a method of and a device for supplying fuel to a rotary piston engine of the type which comprises a casing composed of a rotor housing having a trochoidal inner peripheral surface and side housings which close opposite ends of said rotor housing and a polygonal rotor adapted to rotate eccentrically in said casing with apex portions thereof sliding over said trochoidal surface while defining a plurality of combustion chambers between said trochoidal surface and individual side walls of said polygonal rotor.
2. Description of the Prior Art:
The rotary piston engine of the abovementioned type (Wankel-type) has, due to its particular combustion process, a feature that, although the HC and CO content in the exhaust gas are relatively high, the content of NOx is relatively low when compared with the conventional reciprocating piston engine. This feature of the rotary piston engine is utilized for providing a low air pollution engine, wherein HC and CO are eliminated by the recombustion of said constituants in a thermal reactor while the content of NOx is primarily low enough to satisfy the current regulations without any treatment therefor. However, it is expected that the regulations regarding the exhaust gas of automobiles will become stricter in the future. Therefore, the present rotary piston engine will soon exceed the limitation regarding the amount of NOx.
It is known that generally there is a relationship such as shown in FIG. 1 between the air/fuel ratio and the emission of HC, CO and NOx in the exhaust gas of a gasoline engine, although in FIG. 1 the scales for CO, HC and NOx are particularly adapted for the case of the rotary piston engine. As is apparent from FIG. 1, the NOx content in the exhaust gas becomes maximum when the air/fuel ratio is 15-16 and lowers relatively steeply as the air/fuel ratio increases or decreases from the abovementioned value. The present anti-air pollution rotary piston engine employs air/fuel ratio of about 12-13, whereby the emission of NOx is restricted within an acceptable limit while the HC and CO delivered in this operational condition are eliminated by recombusting the same in a thermal reactor. However, if, for example, the limit value of 0.25 g/km for NOx, which is expected to be enforced in the near future, is to be satisfied, the NOx content must be lower than 130ppm. To accomplish this, the air/fuel ratio must be either substantially low like the order of 11-12 or, on the contrary, relatively high like the order 18-19. If the air/fuel ratio is lowered to the order of 11-12, the amount of HC and CO substantially increases beyond the limit which can be processed by the present thermal reactor or catalyst. On the other hand, if the air/fuel ratio is increased so high as 18-19, the ignitability of fuel/air mixture becomes so poor as to cause misfiring and to make it difficult to maintain smooth operation of the engine. In this condition, the CO content is almost zero and although the amount of HC relatively increases when compared with its minimum value, its absolute value is still acceptable and it is possible to process the uncombusted components by the present thermal reactor or catalyst.